Meninges

What are meninges?

Meninges are three layers of membranes that cover and protect your brain and spinal cord (your central nervous system [CNS]). They’re known as:

• Dura mater: This is the outer layer, closest to your skull.
• Arachnoid mater: This is the middle layer.
• Pia mater: This is the inner layer, closest to your brain tissue.

Together, the arachnoid mater and pia mater are called leptomeninges.

There are three spaces within the meninges:

• The epidural space is a space between your skull and dura mater and the dura mater of your spinal cord and the bones of your vertebral column. Analgesics (pain medicine) and anesthesia are sometimes injected into this space along your spine. The spinal cord ends between the first and second lumbar vertebra in the middle of your back, at which point, only cerebrospinal fluid is present. This is the site where a lumbar puncture (“spinal tap”) is performed.
• The subdural space is a space between your dura mater and your arachnoid mater. Under normal conditions, this space isn’t a space, but can be opened if there’s trauma to your brain (such as a brain bleed) or other medical condition.
• The subarachnoid space is a space between your arachnoid mater and pia mater. It’s filled with cerebrospinal fluid. Cerebrospinal fluid cushions and protects your brain and spinal cord.

What do the meninges do?

The meninges:

• Protect your CNS (central nervous system) from trauma injury to your brain, such as a blow to your head by acting as a shock absorber. They anchor your CNS and keep your brain from moving around within your skull.
• Provide a support system for blood vessels (including your middle meningeal artery) that deliver blood to your CNS tissues, nerves (including your trigeminal and vagus nerves), lymphatics (drainage system) and cerebrospinal fluid.

What are the features of dura mater?

Your dura mater is the outer, thick, strong membrane layer located directly under your skull and vertebral column. In Latin, dura mater means “hard mother.” It consists of two layers of connective tissue. One side of your dura attaches to your skull and the other adheres to your middle membrane layer (arachnoid mater). Your dura mater contains a drainage system, called the dural venous sinuses, which allows blood to leave your brain and allows cerebrospinal fluid to re-enter the circulation. Your dura mater receives its blood supply from your middle meningeal artery and vein, and your trigeminal nerve runs through it.

Your dura mater folds inward onto itself to form four thin membrane layers called dural reflections. Each dural reflection surrounds different sections (hemispheres) of your brain.

What are the features of arachnoid mater?

Your arachnoid mater, the middle layer of your meninges, lies directly below your dura mater. It’s a thin layer that lays between your dura mater and pia mater. It doesn’t contain blood vessels or nerves. It has a spiderweb-like appearance (“arachnoid” means spider) because it has connective tissue projections that attach to your pia mater. Between your arachnoid mater and pia mater is the subarachnoid space, which contains cerebrospinal fluid that helps cushion your brain.

What are the features of the pia mater?

Your pia mater, the innermost layer, is a thin layer that’s held tightly — like shrink wrap — to the surface of your brain and spinal cord. Many blood vessels pass through this layer to supply your brain tissue with blood. It also helps contain cerebrospinal fluid. In your spinal cord, pia mater helps maintain the stiffness of the cord.

What medical conditions affect the meninges?

Two of the more common conditions that affect your meninges are:

• Meningitis. This is an infection of your meninges. The infection can be caused by bacteria, fungus or viruses. A lumbar puncture to get a cerebrospinal fluid sample is usually required to diagnose this condition. Rarely, meningitis can occur by non-infectious causes such as cancers, inflammatory disease, brain surgery or certain medicines.
• Subdural hematoma. This is bleeding that occurs between your dura mater and arachnoid mater due to a tear in a blood vessel.
• Bleeding within other meningeal layers. Many blood vessels travel through your meninges. Trauma to your head can cause bleeding between any of the layers of meninges, especially in people who take blood thinners or have bleeding disorders.

Other medical conditions affecting your meninges include:

• Meningiomas. These are tumors that grow in your meninges. They’re usually not cancerous, but can grow large enough to be life-threatening and may require surgical treatment.
• Meningeal carcinomatoses. This is cancer that has spread from its original tumor site to your meninges.

There are many other conditions that can affect each specific meningeal layer. Because of the important role of your meninges in protecting your brain, conditions that affect your meninges can be potentially life-threatening.

A note from Cleveland Clinic

Your brain and spinal cord are protected and supported by three meningeal layers. These membrane layers are the dura mater, arachnoid mater and pia mater. The layers plus cerebrospinal fluid keep your brain tissue from jostling against your skull, as well as other functions. Trauma to your head, however, can cause bleeding within any of your meninges and/or your brain tissue itself (intracranial hemorrhage). Be sure to see your healthcare professional if you experience a blow to your head from a trauma (like a car accident), sports injury or fall.